In a study published today in the British medical journal The Lancet, people following the Weight Watchers regimen for 12 months lost twice as much weight as those who followed the weight-loss guidance of their primary-care physicians.

Researchers in the U.K., Australia and Germany tracked a total of 772 overweight and obese people who sought to lose weight. Roughly half were assigned to follow weight-loss guidance hewing to nationally accepted standards of care and offered by their primary-care doctors. The others were referred by their primary-care doctors to take part, free of charge, in Weight Watchers. After attrition, the first group included 214 people, the Weight Watchers group 230.

By the end of 12 months, those in the Weight Watchers group lost a mean of about 15 pounds (6.7 kg); those under their doctors’ guidance lost just over 7 pounds (3.3 kg). The Weight Watchers group also saw greater reductions in waist circumference and fat mass.

The study identifies regular weigh-ins, advice regarding diet and physical exercise, motivation and group support as key components of the Weight Watchers program. The study notes that participants in the Weight Watchers arm were asked not to reveal their participation in research to their Weight Watchers leaders or others in their Weight Watchers groups.

The study was funded by Weight Watchers through a grant to the U.K. Medical Research Council. The authors state that “the sponsor had no role in the study design, data collection, data analysis, data interpretation, or writing of the report.”

The new findings come at an interesting time in the weight-loss world. Over the past year, two surveys published in the U.S. came to different conclusions as to which commercial weight-loss program works best: Consumer Reports in May named Jenny Craig the most effective, while U.S. News and World Report in June put Weight Watchers at the top of its list. The current study did not compare Weight Watchers to other commercial weight-loss plans.

A commentary accompanying today’s Lancet study suggests that it might prove cost-effective to cover the costs of commercial weight-loss programs such as Weight Watchers as part of publicly-funded health care.